放牧对五台山高山、亚高山草甸植被-土壤系统耦合的影响

Impacts of grazing on the system coupling between vegetation and soil in the alpine and subalpine meadows of Wutai Mountain

以野外样地调查和室内分析的数据为基础,研究了放牧压力下五台山高山、亚高山草甸植被、土壤的变化特征,并利用灰色系统分析法,从群落和物种两个尺度探讨了放牧对五台山植被-土壤系统耦合的影响。结果表明:随着放牧压力的加大,土壤pH、有机质和全氮含量呈先下降后上升的非线性变化,在极度退化草甸下达到最大值;灰色关联分析表明土壤有机质和全氮与群落地上生物量、物种多样性、群落总盖度的关联度较高,土壤有机质、全氮对群落特征变化有一定影响;在受到强度干扰时,植物群落优势物种由原生种向退化种发生替代变化。系统耦合度的定量研究表明,现有的放牧强度已经使五台山山地草甸的植被-土壤系统的耦合水平降低。草甸的退化不仅仅是植被与土壤的衰退,也导致两个子系统耦合关系的减弱,使系统表现出相悖的发展趋势。

The subalpine and alpine meadow vegetation of Wutai Mountain,distributed in altitude from about 2400m a.s.l.through to 306 1m a.s.l.at the summit,serves as the largest summer mountainous pasture for cattle grazing around the local area in Northern China.The degradation of meadow with different grades owing to overgrazing in different extents has been observed in both vegetation and soil.Considering some features of vegetation,i.e.,the coverage,the aboveground biomass,the ratio of annual to biennial plants in species composition,the species richness and the α-diversity index,five grades of meadow degradation relating to different grazing pressure have been recognized in the area through our earlier studies（see Reference No.8）.This paper,through a grey correlation analysis at both species and community levels,evaluated the system coupling between the vegetation and the soil along with the degradation process in the subalpine and alpine meadow vegetation of Wutai Mountain.85 sampling quadrat data,which were collected during the field survey in 2006 with the quadrat sized in 1m×1 m,were involved in the analysis.The results showed that：（1） The pH-value,the content of total organic matter and the content of total nitrogen in soil varied nonlinearly among different degraded communities.The values of these soil parameters decreased with the grazing intensification on vegetation first,and then rose rapidly until reached their maximum in the extremely degraded meadow communities,where the vegetation were almost totally destroyed by overgrazing and tramping,while the soil was in s great extent mixed with cattle feces;（2） Showing in the grey correlation analysis,both the soil organic matter and total nitrogen contents correlated significantly with vegetation features represented by the aboveground biomass,the plant species diversity and the coverage at the community level;（3） The soil features coupled strongly with the species group consisted mainly of Kobresia pygmaea,K.pusilla,Pottentilla niveaand Festuca rubrain the meadow communities influenced by grazing and the slightly degraded meadow communities,whereas in contrast with another group consisted mainly of Potentilla anserine,P.conferta,Axyris amaranthoides,Polygonum aviculareand Cirsium leoin the extremely degraded communities;（4） The system coupling between vegetation and soil varied on average from the high level with index value at about 0.6-0.8 in the communities before being seriously degraded,to the low level at about 0.4-0.6 in those being extremely degraded,implying that the decrease of the system coupling level between vegetation and soil might therefore be an additive indicator to show the seriousness and extremes of degradation for the subalpine and alpine meadow vegetation.